Signal processing device, ultrasound diagnostic apparatus, and signal processing method

Abstract

A signal processing device which uses a first signal waveform of ultrasound reflected from an object in a first compressed state and a second signal waveform of ultrasound reflected from the object in a second compressed state and calculates an elasticity of the object affected by a change in a compressed state includes: a phase difference calculation unit which calculates a phase difference component in each time between the first signal waveform and the second signal waveform; a correlation calculation unit which calculates an elasticity pertaining to a difference in angular frequencies between the first signal waveform and the second signal waveform and an initial phase difference according to a correlation between the each time and the phase difference component in the each time; and an elasticity calculation unit which calculates the elasticity on the basis of the difference in angular frequencies.

What is claimed is: 
     
         1 . A signal processing device which uses a first signal waveform of ultrasound reflected from an object in a first compressed state and a second signal waveform of ultrasound reflected from the object in a second compressed state and calculates an elasticity of the object affected by a change in a compressed state, the device comprising:
 a phase difference calculation unit which calculates a phase difference component in each time between the first signal waveform and the second signal waveform;   a correlation calculation unit which calculates an elasticity pertaining to a difference in angular frequencies between the first signal waveform and the second signal waveform and an initial phase difference according to a correlation between the each time and the phase difference component in the each time; and   an elasticity calculation unit which calculates the elasticity on the basis of the difference in angular frequencies.   
     
     
         2 . A signal processing device which uses a first signal waveform of ultrasound reflected from an object in a first compressed state and a second signal waveform of ultrasound reflected from the object in a second compressed state and calculates an elasticity of the object affected by a change in a compressed state, the device comprising:
 an approximated waveform generation unit which compresses or stretches and phase-shifts the second signal waveform by an elasticity and an initial phase difference related to a difference in angular frequencies being set and generates an approximated signal waveform approximated to the first signal waveform;   a phase difference calculation unit which calculates a phase difference component in each time between the first signal waveform and the approximated signal waveform;   a correlation calculation unit which calculates the elasticity and the initial phase difference between the first signal waveform and the approximated signal waveform according to a correlation between the each time and the phase difference component in the each time;   a repeat determination unit which updates the approximated signal waveform by compressing or stretching and phase-shifting the approximated signal waveform by using the elasticity and the initial phase difference calculated by the correlation calculation unit until a predetermined condition is satisfied, and uses the updated approximated waveform and the first signal waveform to repeat processing by the phase difference calculation unit and the correlation calculation unit; and   an elasticity calculation unit which calculates the elasticity on the basis of a cumulative value of the elasticity related to the compression repeatedly performed.   
     
     
         3 . The signal processing device according to  claim 2 , further comprising a recovery rate calculation unit which calculates a recovery rate indicating a correlation between the first signal waveform and the approximated signal waveform when the predetermined condition is satisfied. 
     
     
         4 . The signal processing device according to  claim 3 , further comprising a display unit and a display control unit which causes the display unit to display the elasticity and calculation accuracy of the elasticity based on the recovery rate. 
     
     
         5 . The signal processing device according to  claim 3 , further comprising a noise removal unit which smoothes a space distribution of the elasticity calculated, wherein the noise removal unit calculates magnitude of the smoothed elasticity in each spatial position by a weighted average of magnitude of the elasticity in each of a plurality of positions within a predetermined range corresponding to the spatial position, and a weight of the weighted average is determined on the basis of magnitude of the recovery rate in each of the plurality of positions. 
     
     
         6 . The signal processing device according to  claim 2 , wherein the phase difference calculation unit changes a width of the time pertaining to the calculated phase difference component according to at least one of the elasticity and the initial phase difference between the first signal waveform and the approximated signal waveform. 
     
     
         7 . The signal processing device according to  claim 2 , wherein the repeat determination unit sets, as the predetermined condition, a case where the elasticity between the first signal waveform and the approximated signal waveform equals a predetermined reference value or smaller. 
     
     
         8 . The signal processing device according to  claim 1 , wherein the correlation calculation unit calculates an optimal value of the elasticity and the initial phase difference by a least squares method using the elasticity and the initial phase difference as parameters. 
     
     
         9 . An ultrasound diagnostic apparatus comprising:
 an ultrasound probe which transmits/receives ultrasound; and   the signal processing device according to  claim 1 .   
     
     
         10 . A signal processing method which uses a first signal waveform of ultrasound reflected from an object in a first compressed state and a second signal waveform of ultrasound reflected from the object in a second compressed state and calculates an elasticity of the object affected by a change in a compressed state, the method comprising:
 a phase difference calculation step which calculates a phase difference component in each time between the first signal waveform and the second signal waveform;   a correlation calculation step which calculates an elasticity and an initial phase difference between the first signal waveform and the second signal waveform according to a correlation between the each time and the phase difference component in the each time; and   an elasticity calculation step which calculates the elasticity on the basis of the elasticity.   
     
     
         11 . The signal processing device according to  claim 2 , wherein the correlation calculation unit calculates an optimal value of the elasticity and the initial phase difference by a least squares method using the elasticity and the initial phase difference as parameters. 
     
     
         12 . An ultrasound diagnostic apparatus comprising:
 an ultrasound probe which transmits/receives ultrasound; and   the signal processing device according to  claim 2 .